The lido is an extremely popular haunt for city-dwellers hoping to cool off.
The 60-acre lake is even described as a ‘secret city beach’.
But the local council has issued a warning for all beach-goers.
The lake is said to be filled with ‘parasites’ that could cause harm to anyone brave enough to jump in, as reported by NeedToKnow.
Brits wanting to cool off in the Ruislip Lido in Hillingdon, west London, may be susceptible to ‘swimmer’s itch’, an irritating skin rash caused by parasites.
A sign at the lido reads: “Do not swim when red flags are present.”
But visitors looking to cool off on Wednesday (14 May) ignored the flags.
Members of the public were spotted splashing around in the water.
Hillingdon Council states: “The beach at Ruislip Lido is open, but swimming is not permitted.
“This is because the shock of cold water can make swimming and getting out of the water difficult.
“The depth of the water changes and is unpredictable.
“Underwater objects and hazards may not be visible.
“Swimmer’s itch can be caused by an allergic reaction to certain microscopic parasites living in the water.”